Don't autotranslate in incognito mode (so we don't send information...

Don't autotranslate in incognito mode (so we don't send information
to the translation server without the user consent).
Also added unit-tests for prefs.

BUG=38107
TEST=Visit a page that triggers the translate infobar. Translate the
     page. Select "Always translate <lang1> to <lang2>".
     Open a page in lang1. The page should automatically be translated
     to lang2.
     Open an incognito window. Navigate to a page in lang1, the page
     should not automcatically be translated, an infobar should ask
     if the user wants to translate the page.


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=42400

[kuan, 2010-03-23 19:02:09]

LGTM.

http://codereview.chromium.org/1184001/diff/1/3
File chrome/browser/translate/translate_manager.cc (right):

http://codereview.chromium.org/1184001/diff/1/3#newcode173
chrome/browser/translate/translate_manager.cc:173: // If the user has previously
select "always translate" for this language we
nit: selected

http://codereview.chromium.org/1184001/diff/1/2
File chrome/browser/translate/translate_manager_unittest.cc (right):

http://codereview.chromium.org/1184001/diff/1/2#newcode649
chrome/browser/translate/translate_manager_unittest.cc:649: // It should have
been triggered an automatic translation to English.
nit: have been -> have